The present invention relates to printing presses and more particularly to a web stabilization apparatus.
In a web fed rotary printing press having multiple printing units, it may be desired to stop printing one or more printing units by throwing the blanket cylinders away from the web. This can permit, for example, a plate or blanket change. Automatic plate changes can occur using an automatic transfer printing unit. Such a printing press is for example manufactured by Goss International as the Sunday 2000 Autotransfer Press.
When the blanket cylinders are separated from the web, the web can pass freely between the two blanket cylinders. As the web passes between the separated blanket cylinders the web may demonstrate out-of-plane vibrations. More specifically, these out-of-plane vibrations occur when the auto transfer unit blankets are off impression and when the web is passing through at normal printing speeds.
When the web experiences out-of-plane vibrations, unintentional web contact can occur with the blanket cylinders. Unintentional web contact with the blanket cylinders could result in print defects on the web or web breakage. It is known in the printing industry to use rollers located upstream and downstream from a printing unit in an attempted to stabilize a moving web. However, rollers can produce marking or damage to the web. U.S. Pat. No. 5,924,619 describes an apparatus for passing a printed web between separated cylinders of a deactivated printing unit.
Referring to FIG. 1A, a prior art printing press 100 is shown with a web 110 and without a web stabilization device. Printing press 100 has printing units 105-1 through 105-a, where a is a predetermined value, preferably 5 or 8 for an automatic transfer press with 5 units having two black printing units and 8 having two printing units each for magenta, cyan, yellow and black. The printing units 105-1 through 105-a each have 4 cylinders, 2 blanket cylinders, 2 plate cylinders and 2 automatic plate changers. Printing unit 105-1 has blanket cylinders 115-1a,b, plate cylinders 120-1a,b, and automatic plate changers 160-1a,b. Print unit 105-2 has blanket cylinders 115-2a,b and plate cylinders 120-2a,b, where all 4 cylinders are rolling without contact, which can permit, for example, automatic plate transfer by automatic plate changers 160-2a,b. As shown in FIG. 1(a), as web 110 moves in the direction denoted by arrow 125, web 110 experiences out-of-plane vibrations (denoted by arrow 130) where unintentional web contact can occur with blanket cylinders 115-2a,b. 
FIG. 1B shows the prior art printing press 100 of FIG. 1A with rollers 130-a and 130-b located upstream and downstream from printing unit 105-2 which is off impression. Web 110 runs over roller 130-a and under 130-b in an attempt to provide out-of-plane web stability. The problem with this configuration is that rollers 130-a,b can produce unacceptable damage to web 110, such as such as damage to the wet printed surface and web breakage.
FIG. 1C shows the prior art printing press 100 of FIG. 1A with rollers 140-a and 140-b located upstream and downstream from the deactivated printing unit 105-2, in an attempt to provide out-of-plane web stability. In FIG. 1(c), the cylinders of print unit 105-2 are inclined away from the vertical angle by an angle of inclination, for example, of 10 to 15 degrees. Like in FIG. 1(b), web 110 runs over roller 140-b and under roller 140-b in an attempt to stabilize moving web 110. As mentioned above, rollers 140-a,b can produce unacceptable damage to web 110, such as damage to the wet printed surface and web breakage.